Sphygmomanometer

ABSTRACT

A container of specific volume is pressurized simultaneously with the inflation of an artery occluding cuff. The container is isolated from the cuff by means of a diaphragm, which after inflation of the cuff, controls bleeding of the cuff pressure in a manner to maintain cuff pressure equal to the container pressure. A fluidic bistable oscillator or flip-flop is connected to bleed fluid from the container through alternating exhaust paths in a manner to produce oscillating mass-flow pulses. The mass-flow pulses are counted as incremental and accumulating pressure values when signals are received from a microphone detecting Korotkoff noises. The counters provide a digital display of systolic and diastolic pressures. Pulse events are utilized to reinforce the detection of Korotkoff signals, and the pulse rate per minute is recorded in a separate register.

United States Patent [191 Buddecke et al.-

[ SPHYGMOMANOMETER Primary Examiner-Kyle L. Howell [75] V Inventors: Charles L. Buddecke, Fullerton; Atomey A"an Fowler at John Le Valley, South Pasadena, 7 both of Calif. ABSTRACT 73 Assignee; A Inc Fullerton, ca]if A container of specific volume is pressurized simul- 1 taneously with the inflation of an artery occluding [22] 197 cuff. The container is isolated from the cuff by means [21] ApplQNo; 189,425 of a diaphragm, which after inflation of the cuff, controls bleeding of the cuff pressure in a manner to v lto the container ressure. s2 U.S. (:1. 128 2.05 M f f f aqua P Int Cl 5/02 A fluidic bistable oscillator or flip-flop lS connected to 58 Field of'; 'c'i;lll 15.92165 M, 2.05 A bleed fluid r the through alternating 128/2 05 R, 2.05 G, 205 P; 13/398, 402 haust paths in a manner to produce oscillating massflow pulses. The mass-flow pulses are counted as in- 5 References Cited cremental and accumulating pressure values when i signals are received from a microphone detecting UNITED STATES PATENTS Korotkoff noises. The counters provide a digitaldis- 3,508,537 4/1970 Kahn etal. ..12s/2.0s A P Siystolic and diastolic P m- Pulse events 3,552,381 1/1971 Burns et al ..l28/2.05A are utilized to reinforce,the detection of Korotkoff 3,623,476 11/1971 Robillard ..l28/2.05 M signals, and the pulse rate per minute is recorded in a 3,536,062 0/1970 H0111 ..128/2.05 R eparate registen 3,581,734 6/1971 Croslin et al ..l28/2.05 M t 31 Claims, 2 Drawing Figures 5PEC/F/6 0; 1,145 5/6/VOL P19066550? tawny/N52 411/0 co/vrear 1 COUNTEES/ D/5'PL/7/ PEES'L/FE 5W/7'CH iatented' May 1, 1973 2 Sheets-Sheet 1 Patented May 1, 1973 kvwvwm a 5 2 sqegt -sheet 2 the memory of the operator.

SPHYGMOMANOMETER This invention relates to an improved method and apparatus for indicating arterial systolic and diastolic ment of blood pressure, an inflatable cuff is wrapped about the subjects upper arm and inflated to a pressure great enough to occlude all blood flow in the brachial artery. A valve is then opened to gradually relieve the occluding pressure. A point is reached where the maximum arterial blood pressure occurring during the periodic closure of the left heart ventricle is equal to the cuff occluding pressure. As the cuff pressure decreases to and subsequently passes such a level, the artery opens for a short interval each heart cycle in a correspondingly short blood pulse flow therethrough. This equal pressure point identifies the subjects systolic blood pressure.

A stethoscope or similar device is placed on the artery at the subjects forearm, a point more remote or downstream from the heart than the occluding cuff. The artery walls expand responsive to each blood pressure and give rise to what has been designated as Korotkoff audible sounds which are detected via the stethoscope. The operator, upon auditorily noting the inception of these sounds, quickly visually reads the corresponding instantaneous value on a pressure manometer column connected to the cuff. This yields the systolic blood pressure.

. As the cuff occluding pressure decreases further, the diastolic point is reached where the artery remains open for essentially the entire cardiac cycle. Accordingly, the distinct audible sounds generated by the intermittent blood flow essentially disappear after the diastolic point is reached. Hence, after the operator notes the auditory disappearance of the Korotlroffv sounds, he again visually reads the instantaneous pressure to derive the subjects diastolic pressure.

The major difficulty of this technique, which has long been recognized, is that it requires considerable subjective judgment on the part of the operator, both in detecting the Korotkoff noises and in visually reading the moving manometer column. Also, manometers are not very accurate, and the reading is not retained except by The prior art includes a large number of systems for automating various steps in the blood pressure measur ing process. In one example of this, a stethoscope is replaced by a microphone to produce electrical pulse replicas of the Korotkoff sounds occurring while the pressure in an occluding cuff traverses between the subject's systolic and diastolic values. Suitable meters are latched to systolic and diastolic indications at the inception and termination of the electrical pulses. Although these various prior art automated systems have certain advantages, the fact remains that the most common system for measuring blood pressure is still the'manual system outlined above. It is believed that a need still exists for a reliable and simple automated system which generates accurate reproducible and retainable blood pressure readings.

In accordance with this invention, the conventional technique for indirect measurement of systolic and diastolic blood pressure is implemented by a unique combination of a bistable fluidic flip-flop device and electronic counters to convert the pressure values directly into digital numbers. A container of specific volume is pressurized to the same level as an artery occluding cuff to become in effect a fluidic capacitor, and pressure is bled from the container through the fluidic device. Although a single pressurizing means, such as a hand bulb, may be employed to pressurize both the container and the cuff, the container is isolated from the cuff. This may be accomplished by means of an pneumatic diode to fill thecuff from the container and an interface device that controls the bleeding of pressure from the cuff so that its pressure is maintained substantially equal to container pressure.

The flip-flop device produces oscillating equal pressure pulses that can be counted to provide a measure of the pressure in the container and hence the pressure in the cuff. By initiating the counting operations at the appropriate times, corresponding to detected signals of the systolic and diastolic events, direct digital readings of these pressure values are obtained.

In a preferred approach, the systolic and diastolic event signals are simply obtained by means of a microphone detecting the presence and absence of the Korotkoff noises. The authenticity of these signals is further reinforced by detecting the heart generated arterial pressure pulse so that the electronic counters are reset and initiated only when the dual signals are obtained thus the instrument knows when to listen. Also the pressure pulse signal is electronically processed to provide a separate digital numerical display of the pulse beats per minute.

The container may be advantageously filled from the pressurizing source and the cuff from the container through a pneumatic diode which introduces a pressure drop in the filling process. Consequently a pressure responsive device is provided to sense this pressuredifferential and indicate when the pressure is falling in the cuff, and hence initiates the measurement cycle. Once the cycle has begun electrical means are provided to reset the counters at the appropriate times corresponding to the systolic and diastolic events.

For a more thorough understanding of the invention refer to the following detailed'description and drawings in which:

FIG. 1 is a diagrammatic and schematic illustration of the overall pneumatic and electronic system of the invention; and

FIG. 2 is a schematic, more detailed, view of the electronic components of the invention; 7

As can be seen in FIG. 1 there is provided a pneumatic system 8 including a pumping means such as a,

hand squeeze bulb 10 having an inlet check valve connected by a tube 12 through a check valve 14 and a pneumatic diode 16 to an inflatable cuff 18, adapted to be wrapped around the arm, or other extremity, of a subject whose blood pressure is to be measured. A container or reservoir 20 of a specific, fixed volume is connected by a tube 22 to the tube 12:: between the check valves 14 and 16. Connected inparallcl to the tube 12 around the valve 16 is a tube 24 connected to a pressure equalizing interface device 26.

The device 26 includes a casing or housing 27 divided into two chambers 27a and 27b having equal internal diameters by a common flexible diaphragm 28.

As can be seen, the chamber 27a is in open communispecific volume container, while the chamber 27b is in communication by way of the tubes 24b and 12b with the cuff 18. An exhaust vent 30 open to the chamber 27b is provided for bleeding pressure from the cuff 18. A valve member 32 carried by the diaphragm 28 controls the flow of air from the chamber 27b through the exhaust vent 30. The diaphragm 28 is constructed such that when the pressures within the chambers 27a and 27b are equal the valve member 32 closes the vent 30.

A bistable, fluidic flip-flop device 34 is schematically shown connected by a tube 36 to the fixed volume container 20. The flip-flop 34 includes an inlet port or passage 34a which leads to a common junction 34b connected to a pair of output ports or paths 34c and 34d. The output port 34c is connected by a tube 38 through a restrictor 40 and a tube 42 to a control port 34, which connects to the junction 34b. Similarly the output port 34d is connected by a tube 44 through a restrictor 46 to a tube 48 leading to a control port 34f, which connects to the junction 34b opposite from the control port 34e. An exhaust port or path 34g is connected to the outlet port 340. A similar exhaust port or path 34h is connected to the outlet port 34d. The two exhaust ports vent directly to atmosphere. The outlet ports 34c and 34d are further connected to a differential pressure operated electrical switch 50, which provides the means for converting pneumatic pressure pulses into electrical signals.

Also included in the pneumatic circuitry is a differential pressure operated electrical switch 52 connected by a tube 54 to the tube 36 leading to the fixed volume container, and by tubes 55 and 56 to the cuff 18. The switch 52 connection is such that it is normally electrically open, and is electrically closed when the pressure in the cuff 18 is higher than the pressure in the container 20. This condition occurs when the pressure inthe cuff l8 commences to follow the falling pressure in the container 20.

For detecting Korotkoff sounds a microphone or transducer 58 is positioned distally in the cuff 18 or just downstream of the cuff on the subjects arm or leg and overthe brachial artery area. A pressure transducer 60 is connected to the cuff by way of the tube 55 to detect the subjects heart pulse.

Turning now to the electrical circuitry, the output of the pressure operated switch 50 is connected by a conductor 51 to registers of the digital counter/display 61. One terminal of the pressure differential switch 52 is connected by a conductor 53 to the counter/display 61. The other terminal is connected by a conductor 64 to the signal processor and control 62. The electrical output from the microphone 58 is connected by a conductor 59 to the signal processor and control 62 for the purpose of processing systolic and diastolic event signals. Also fed into the signal processor control through conductor 63 are signals from the transducer 60. The output of the signal processor and control 62 is fed to the digital counters and display 61 upon which systolic and diastolic pressures are registered together with the subject's pulse in beats per minute.

Refer now to FIG. 2 for a further description of the major components within the signal processor and control 62 and the counters and display 61. The microphone 58 is connected by the conductor 59 to an impedance matching amplifier 113 and then to a linear amplifier 65, having a transfer function determined by a band stop filter network 66. The signal from the amplifier 65 is fed to a display circuit 1 16 which operates a light or a display to indicate the Korotkoff signals in both the inflating cycle and the measurement cycle. This signal from amplifier 65 is fed also to an analog gate 67, which is serially connected through a one-shot circuit 68, to a dynamic latch leading to a systolic and pulse reset driving circuit 72. A diastolic reset and pulse reset driving circuit 74 is also connected to the output of the one-shot circuit 68 and is in parallel with the dynamic latch 70.

The arterial pressure transducer 60 is connected by the conductor 63 to an impedance matching amplifier 114 and then to a linear amplifier 76, having a transfer function determined by a high pass filter network 78, and further connected to a one-shot circuit which has its output fed to the analog gate 67. The gate 67 also receives an input from a sequence latch 82 that receives an input from a set circuit 112 through the conductor 64 connected to the differential pressure switch 52. The sequence latch 82 is linked to a systolic timing circuit 84 and the output of the dynamic latch 70 through a gate 115. The output of the dynamic latch 70 is also connected to a pulse rate driver circuit 86 which is linked to an AND gate 90. The one-shot circuit 80 is also linked through a driving circuit 88 to the AND gate 90. The gate output signal is fed to a times 3 circuit 92, and a pulse count driving circuit 94.

The pulse count driving circuit 94 is serially connected to decade counters 96a, 96b and a flip-flop 96c in the counter/display 61. The pressure switch 50 is connected to the differential switch 52 by the conductor 51, a driver circuit 111, and the conductor 53. The output signal from the driver circuit 111 is further connected to the ready light circuit 116 and to the input of decade counters 98a and 98b, flip-flop 98c, decade counters 100a and 100b and flip-flop 100a. The systolic and pulse reset driving circuit 72 is connected to reset the systolic pressure decade counters 98a and 98b and the flip-flop 98c, and to reset the pulse count decade counters 96a and 96b and the flip-flop 960. The diastolic reset driving circuit 74 is connected to reset the decade counters 100a and 10% and flip-flop 1000:. The output of the flip-flops 96c, 98c and 1000 are connected respectively to the multiplexers 104a, b and c, decoder drivers 1064, b and c and individual display devices 108a, b and c. A series of display select switches 110 are connected to the multiplexers 104 for manual selection of the appropriate display counter.

The circuitry may be conveniently operated by batteries to make the system readily portable, but for purposes of simplicity the power supply is not shown.

OPERATION In operation the operator repeatably squeezes the hand bulb pump 10 in normal fashion to inflate the cuff 18 which has been properly fitted around the subjects arm or leg. As indicated above, pressure can flow through the one-way valve 14 and the pneumatic diode 16 to the cuff but reverse flow is prevented. Simultaneously with the inflation of the cuff, the known volume reservoir 20 is pressurized directly by the bulb 10 through the check valve 14 and tube 22. This arrangement is advantageous in that the container acts as a dampener for the cuff so that the cuff inflates smoothly instead of with surges of pressure, this is more comfortable for the subject.

The operator will continue to pump the bulb until the brachial artery in the arm is completely occluded by virtue of the pressure in the cuff being higher than systolic blood pressure. An operator will know when this condition has been reached by the signal indicator light 117 connected .to the microphone 58 so that the light will flash with each acoustical pulse as the system detects the Korotkoff sound during the transition between diastolic and systolic pressure during inflation of the cuff. When the pulse flash is no longer observed, the operator ceases inflation; and the system deflates through the operation of the fluidic oscillator 34 and the vent 30. Although pressure in the container operates the flip-flop 34 during inflation of the cuff, the rate at which the air is being processed from the container is so much slower than the rate the cuff and container are being pressurized by the bulb, that the processed flow is insignificant.

As air is processed from the container through the flip-flop 34, the flow will be through the inlet port to either the output port 34c or 34d. The flow attaches to one side or other of the junction 34b and then passes into the output port on that side. The initial selection will be determined at random as is a characteristic of the flip-flop. Assume for purposes of discussion that the flow initially passes into the output port 340. A portion of the flow is vented to atmosphere through the exhaust port 343. Since the exhaust path 34g is restricted in size a pressure buildup occurs in the outlet port 34c and its connecting passage 38 having the restrictor 40 leading to the control port34e. At a consistent point the pressure in the control port 34c becomes sufficient to deflect the fluid flow at the junction 34b to the other side of the passage so that the flow flips over into the outlet port 34d. The same thing then happens on that side of the flip-flop with the result that the fluid flow oscillates between the output ports 34c and 34d. These oscillating flows create oscillating pressures between the output ports which are converted to electrical signals by the differential pressure switch 50. These signals are transmitted by the conductor 51 to the counters 90 and 100.

The output from the switch 50 is transmitted to the ready light circuit 116 causing the light 117 to be energized. This tells the operator that the flip-flop 34 is oscillating. The output from the switch is also fed to the counters 98 and 100 in the display 61 causing the oscillations to be counted. These measurements are meaningless however in that the-counters have not yet been reset at the proper time. The flip-flop 34 operates as a tidal volume oscillator when in this configuration and at low flow rates, such that the flow is laminar in the flip-flop. The device will change state for equal quantities of mass air flow. These quantities are proportional to equal increments of pressure and the device is conveniently calibrated such that one pulse is equivalent to an increment of one millimeter of mercury to indicate differential pressure directly by counting the pulses.

The flip-flop oscillator 34 will continue to operate in this fashion until a minimum operating pressure at the input 34a is reached. This minimum pressure is determined by the pressure drops in the fixed restrictor 37 and variable restrictor 39 operating on the air flow from the container 20 and the decreasing pressure in the container. At this minimum pressure, the differential pressure is insufficient to operate the switch 50 and the digital value of this minimum pressure is automatically added to the pressure pulses counters by resetting the counters to this digital number. When signals from the switch cease, the light 117 goes off telling the operator that the measurement is over.

As air is being processed from the container 20, the pressure in the chamber 27a also drops since they are directly connected. Also, the diaphragm 28 in the interface device 26 maintains the pressure in the cuff essentially proportional to the pressure in the container by allowing air to be bled from the chamber 27b which is connected to the cuff 18. In the arrangement shown, the proportion is one to one in that the areas on both sides of the diaphragm are essentially equal. The compliancy of the diaphragm 28 is :such that very small pressure differentials will operate the valve member 32 controlling the vent 30. Thus the pressure in the cuff will track the decreasing pressure in the container very accurately. The pneumatic diode 16 and the diaphragm 28 prevent any flow of air from the cuff to the flip-flop 34 and so the two systems operate independently, but are at the same instantaneous pressure.

Sincewith the arrangement shown, Korotkoff noises can be detected both when the cufi pressure is being increased and when decreased, it is necessary to known which condition is occurring. This can be accomplished manually, but in the system shown it is detected automatically. With no pressure in the system, there is no differential pressure across the switch 52 and it is electrically open. As the bulb 10 is operated, pressure increases in the container 20 and through the restrictor 37 and the tubes 36 and 54 to one side of the switch 52. Air from the container flows through the pneumatic diode 16 to inflate the cuff 18. However, due to the flow resistance of the diode 16 and the resilience of the cuff 18, thepressure in the cuff 18, and hence in the tubes 56 and S5, lags considerably the pressure in the tube 54 even with the presence of the restrictor 37. Consequently, the switch 52 remains open as the cuff is being inflated and no signals are passed to the set circuit 112 which operates on the sequence latch 82 to insure that blood pressure measurements are not made during inflation. Once inflation is stopped, the pressure in the cuff becomes essentially equal to that of the container 20. Since air in the container is being processed through the fluidic device 34, the pressure downstream of the restrictor 37, and hence in the tube 54, becomes less than that in the tube 55. This differential causes the switch 52 to close electrically. The resulting signal fed to the set circuit 112 and the sequence latch 82 is used to indicate that it is proper to start detecting the systolic and diastolic events. Thus the switch 52 indicates when the pressure in the cuff is falling, which is when measurements are to be made.

The electrical connection between the oscillator switch 50 and the differential switch 52 through the driving circuit 111 insures that the differential switch is only rendered effective'when the fluidic device 34 is functioning. Thus, if the switch 52 should be inadvertently closed, such as might occur if residual air in the cuff were compressed when not on the subjects arm, the momentary closing of the switch 52 would NOT indicate that new measurements were to be made.

in addition to providing a greater pressure differential for the switch 52, the restrictor 37 contributes to the pressure drop with the variable restrictor 39 in the flow of air from the container 20 to the fluidic oscillator. The variable restrictor 39 allows adjustable control of the minimum pressure for operation of the pressure switch 50.

As indicated above, the transducer 60 detects the subjects pulse. This signal is amplified by the linear amplifier 76, and the transfer function is shaped by the high pass filter 78 in the inverse feedback loop. The resulting signal triggers the one-shot circuit 80 which sets the threshold and assures a consistent output used to operate the analog gate 67 in the audio system which will now open as the sequence latch 82 was previously opened by the switch 52 and the set circuit 112.

The microphone 58 detects the Korotkoff sounds which occur when the blood commences to rush through the partly occluded artery as the cuff pressure is falling. The signal from the microphone 58 is amplified by the linear amplifier 65, and the transfer function is controlled by the band stop filter 66 in the inverse feedback loop. The resulting signal is also fed to the gate 67. Coincident signals from both the amplifier 65 and the one-shot circuit 80 operate the gate 67 to trigger the one-shot circuit 68. That is, the sounds detected by the microphone 58 should occur coincident with the pulse beat detected by the transducer 60. The output from the one-shot 68 causes the dynamic latch 70, which operates the systolic and pulse reset driver 72, to reset the electronic counters 98a, 98b and 980 that count the fluidic oscillator signals which the counters receive from the pressure switch 50 and to reset the counters 96a, 96b, and 96c that count signals from the pulse count driver 94.

The dynamic latch 70 has a time period of approximately 2 k seconds=in this set position. This is the longest expected interval between two periods of a continuously pumping heart and accommodates the possibility of a single missed beat in a nominal sequence. Should no other signal appear at the input of the latch during that time period, the latch will reset and the next pulse from the one-shot 68 will again reset the counters upon triggering the dynamic latch. The sequence latch 82 is prevented from turning off the analog gate 67, and

therefore not allowing retriggering of the dynamic latch, by the blocking action of gate 115. The time of the blocking action is controlled by the systolic timing circuit 84 which has an active time of 7 seconds and is initiated by the set position of the dynamic latch 70. This is discussed in greater detail below. If sequential pulses do appear as in the case of a nominal measurement, the latch will remain on and the count will accumulate in the pressure measuring system. Therefore, false signals which would indicate a false systolic event will be rejected if they occur more than 2 ,6 seconds before the true systolic event.

The signal from the one-shot 68 also operates the diastolic reset driver 74 to reset the diastolic counters 100a, 10012 and 1000. This operation occurs each time that the pressure pulse and the Korotkoff sounds coincide, until the sounds no longer trigger the one-shot 68.

Then the diastolic counters continue to count, undisturbed by reset signals. In other words the system has sensed the absence of the Korotkoff sounds by way of the microphone 58, and this absence of sound occurred simultaneously with another pressure pulse detected by the transducer 60.

As indicated above it is also desirable to have a digital reading of the subjects pulse. This is obtained by employing the output of the pressure signal from the one-shot to operate the driver circuit 88, with its output being applied to the input of the AND gate 90. The signal provided by the dynamic latch 70 resets the systolic counters 98 and the pulse counters 96 through the systolic and pulse reset driver 72, and is further applied to initiate the pulse rate timer 86. When the pulse rate timer 86 is on, following the systolic decision and this event is applied to the other input of the gate 90, the pulse signal is transferred to the times 3 circuit 92. This'circuit generates 3 pulses for each one from the transducer 60. This series of 3 pulses for each pulse input is generated for the period of the pulse rate timer 86 which is 20 seconds. Hence the count for the equivalent of one minute is generated and coupled by the pulse count driver 94 to the pulse counters 96a, 96b

and 96c.

It is desirable that the blood pressure and pulse readings obtained be retained in the system until new measurements are to be made. For example, this enables the operator to conveniently repeatedly refer to the data while discussing the results with the patient. Hence, once the diastolic event has occurred it is desirable to close the gate 67 until a new measurement is to be made in that signals which would reset the counters can be generated by extraneous noise and pressures such as might occur when the cuff 18 is being removed. The sequence latch 82 is included to control the gate 67, and thus cause false events to be rejected.

As mentioned above, the diastolic event is indicated by the absence of signals from the gate 67. The dynamic latch 70 also recognizes this event when signals are interrupted, thus causing the latch 70 to reset. it is this resetting of the latch 70 which occursat the end of a true systolic to diastolic event which is used to control the sequence latch 82.

The event of the systolic detection and the operation of the dynamic latch 70 applies a signal to the systolic timer 84 and an input to the gate 115. As mentioned above, the gate prevents the signal from operating the sequence latch 82 to close the gate 67 The systolic timing circuit 84 is also activated by the signal from the latch 70, causing the circuit to hold the gate 115 in the off state for a period of approximately 7 seconds. This is almost as long as the typical systolic to diastolic period with the system disclosed. Consequently, .a systolic event which is not followed by seven seconds of Korotkoff sounds before diastolic occurs would be rejected as a false event, which would be the case if an undesired noise input occurred above the true systolic event.

When the true diastolic event occurs, the resetting of the dynamic latch 70 produces a signal which is conducted through the gate 115 to the sequence latch 82 causing it to close the gate 67. This condition remains until such time as the set circuit 112, after receiving the appropriate signal from the switch 52, causes the latch 82 to unlock the gate 67.

' coupled to the multiplexers 104 for units, tens and hundreds; and by using switch logic, the multiplexers select the counters to be coupled to the decoder/drivers 106 for units, tens, and hundreds from the systolic, diastolic or pulse counter registers. The drivers 106 operate the digital displays 61a, 61b and 610 to present the decimal numbers equivalent to the blood pressures and pulse count measured by the system. In the arrangement illustrated, the operator need merely select one of the switches 110 to obtain the desired numerical display.

As mentioned above, the operator knows when they measurement is complete by the fact that the light 117 turns off.

From the foregoing it can be seen that the fluidic flipflop device 34 is a critical portion of the system. One

that has worked quite satisfactorily is made by Corning Fluidic Products, a Department of Coming Glass Works of Coming, New York. Also it should be noted that while this device presently does not include the fluid restrictors 40 and 46 nor the tube connecting these restrictors to the flip-flop 34, it should be understood that these components could be incorporated into a single fluidic device with the input simply connected to the container 20 and the output connected to the pressure switch 50.

What is claimed is:

1. In a sphygmomanometer having an inflatable cuff to be wrapped around a subjects extremity and pressurizing means for inflating the cuff, an improved means for indirectly determining blood pressure comprising:

. a specific volume container having an inlet means for pressurizing said container; fluidic means connected to said container to process fluid from the container in a manner to produce pressure pulses of substantially equal pressure increments;

isolating means for maintaining the pressure in the cuff proportional to the pressure in the container and for preventing fluid flow from the cuff to the container; and

means for counting the pressure increments to obtain a digital measure of the pressure in the container and thereby pressure in the cuff so that blood pressure can be determined upon receipt of signals related to the events in the indirect measurement of a subject's blood pressure.

2. The sphygmomanometer of claim 1 wherein said fluidic means includes a bistable fluidic flip-flop having an inlet port connected to the container, a pair of output ports stemming from a common junction leading from the inlet port, a pair of restricted exha'ust paths leading from the output ports, a pair of control ports on opposite sides of said junction for deflecting fluid flow to one or the other output port, and a pair of flow restrictors each connecting an output port to one of the control ports to produce said pressure increments.

3. The sphygmomanometer of claim 1:

including means for detecting Korotkoff sounds which occur when the blood first rushes through an artery after the pressure in the cuff has been raised to a level to completely occlude the artery and pressure in the cuff has then been reduced to permit blood to begin to flow through the artery, and means for detecting the absence of Koro'tkoff sounds which occur when the artery is no longer obstructed; and

wherein said counting means includes a counter for registering systolic blood pressure and a counter for registering. diastolic blood. pressure; and includ mg signal processor having means for utilizing the systolic event for operating the systolic counter so as to obtain a systolic blood. pressure reading on the counter and means for utilizing the diastolic event to enable the diastolic counter to obtain a reading of diastolic blood pressure.

4. The sphygmomanometer of claim 3 including means for detecting the subjects pulse and means for utilizing the pulse signal with the Korotkoff signals so that the decision of systolic and diastolic pressures is made by correlating the Korotkoff signals and the pulse signals so that extraneous acoustical signals will not cause erroneous decisions.

5. The sphygmomanometer of claim 4 including electrical ineans for counting and multiplying the pulse signals to obtain a pulse reading in beats per minute.

6. The sphygmomanometer of claim 3 including means for resetting the systolic pressure counter when the Korotkoff sounds indicating the systolic event are first detected, and means for resetting the diastolic counter each time Korotkoff sounds are detected so that cessation of the sounds will indicate the diastolic event and will stop further resetting of the diastolic counter so that the diastolic counter will accumulate the count.

7. The sphygmomanometer of claim 1 including:

means for indicating when the pressure in the cuff is in the systolic-diastolic blood pressure range; v wherein said counting means includes a'counter for registering systolic blood pressure and a counter for registering diastolic blood pressure; means for resetting the systolic counter when the cuff pressure is at systolic pressure; and

means for resetting the diastolic counter each time a signal is received from the indicating means that thecuff pressure is in said range so that when the signals cease at the diastolic event the diastolic counter continues to accumulate the pressure count.

8. The sphygmomanometer of claim 7 including latch means for preventing resetting of said systolic counter once systolic pressure is reached and so long as periodic signals are received by the latch means indicating that the cuff pressure is in said range.

9. The sphygmomanometer of claim 1 wherein said isolating means includes a diaphragm having one side forming the wall of a chamber in communication with the container and having its other side forming a wall of the chamber in communication with the cuff, said diaphragm supporting a valve member for bleeding pressure from the cuff as the pressure is bled from the container.

10. The apparatus of claim 1 including signaling means for indicating when the fluidic means is operatmg.

11. The sphygmomanometer of claim 1 wherein said container is connected to be pressurized as the cuff is being inflated, and including apneumatic diode connected between the cuff and the container permitting flow into the cuff but preventing flow out of the cuff, the diode having significant internal resistance to flow such that air flows smoothly into the cuff.

12. Blood pressure measuring apparatus comprising:

an inflatable cuff to be wrapped around the subjects extremity;

a specific volume container to be pressurized to the level of the inflated cuff while isolated from the cuff;

means for pressurizing said cuff and said container;

means for bleeding fluid from the cuff while maintaining the pressure in the cuff substantially equal to the pressure in the container;

a bistable fluidic flip-flop means connected to said container to process fluid from the container in a manner to produce decreasing asynchronous output pressure pulses of substantially equal pressure increments;

pressure operated switch means responsive to said oscillating pressure increments;

display means including a systolic counter and a diastolic counter for counting the signals received from said oscillator switch means;

a microphone means associated with said cuff for detecting the Korotkoff sounds which occur when the blood first rushes through an artery after the pressure in the cuff has been raised to a level to completely occlude the artery and the pressure in the cuff has then been reduced to permit blood to begin to flow once more through the artery; and

an electronic processor means for processing signals received from the microphone to reset the systolic counter when a signal is received from the microphone indicating that the cuff is at systolic pressure and to subsequently reset the diastolic counter when signals from the microphone are present as defined by Korotkoff until the cessation of such signals indicating that the pressure in the cuff is at diastolic pressure.

13. The apparatus of claim 12:

including a transducer means for detecting the subject's pulse; and wherein said processor means includes means for processing the pulse signals from the transducer in a manner such that signals from the microphone must coincide with the pulse signals before said counters can be reset.

14. The apparatus of claim 12 wherein said processor means includes an electrical gate which receives signals from said microphone means and said transducer means and which will not open unless both signals are present at approximately the same time, the output signal from said gate being utilized to initiate resetting of said counters.

15. The apparatus of claim 14 wherein:

said processor means further includes electrical means for processing the pulse signals received from the transducer to determine the subjects pulse in beats per minute; and

said display means further includes a counter for counting and displaying the subjects pulse directly in beats per minute.

16. The apparatus of claim 12 wherein said processor meansincludes dynamic latch means connected to said microphone and said systolic counter for preventing further resetting of the systolic counter, after the initial resetting indicating systolic pressure, so long as signals from the microphone are received by the latch means in a time interval slightly greater than the interval between two periods of the subjects nominal heart beats.

17. The apparatus of claim 12:

including a restrictor in a tube connecting the container and the fluidic device and a pressure differential responsive switch exposed to the cuff pressure and the pressure downstream from the restrictor to detect when the pressure in the cuff is falling; and

said processor means includes means for processing the signal received from said differential switch to prevent resetting of the counters after the occurrence of the systolic and diastolic events until such time as a signal is received from said differential switch indicating that the pressure in the cuff is once more falling.

18. The apparatus of claim 17 wherein the means within said processor for preventingresetting of the counters until a proper signal is received from said differential switch includes latching means which receives a signal upon indication of the diastolic event and prevents the resetting of said counters until such time as an appropriate signal is received from said differential switch.

19. The apparatus of claim 12 including means for preventing the processor means from providing signals to reset the counters after the diastolic event during the deflation cycle and until a new deflation cycle is in- I itiated.

20. The apparatus of claim 12 including signalling means for indicating when Korotkoff sounds start and cease.

21. A sphygmomanometer comprising:

an inflatable cuff to be wrapped around the subjects extremity;

pressurizing means connected to inflate the cuff;

a known volume container connected to said pressurizing means to be pressurized simultaneously with the inflation of the cuff;

a pneumatic diode in the line between the pressurizing means and the cuff permitting fluid flow into the cuff but preventing fluid flow from the cuff to the pressurizing means or to the container;

a bistable fluidic flip-flop device having an input port connected to said container, the device having a pair of output ports connected to a common junction in communication with the input port, a restricted exhaust path leading from each of said output ports, and a control port on opposite sides of the common junction to oscillate the flow between the two outlet ports upon the application of alternate pneumatic control signals, each control portbeing connected by a restrictor to a respective one of said outlet ports so that as the pressure rises within an outlet port a pressure pulse is created for oscillating the fluid flow to the other outlet port;

an interface device comprising a housing have a flexible diaphragm dividing the housing into a pair of chambers, one chamber being connected to the reservoir and the other chamber being connected to the cuff, an exhaust port being formed in a wall of the chamber connected to the cuff, and a valve member carried by the diaphragm for permitting air to be bled from the cuff at a rate to maintain the pressure in the cuff equal to that of the pressure in the reservoir;

a microphone means for detecting Korotkoff sounds through the artery as the pressure from the cuff is bled from a point above systolic blood pressure;

electrical means for counting the oscillating pressure pulses produced by the fluidic flip-flop device upon receiving a signal from the microphone that Korotkoff sounds corresponding to systolic blood pressure have been detected;

electrical means for counting the pressure pulses produced by the fluidic flip-flop upon receiving a signal from the microphone corresponding to diastolic blood pressure; and

the counting means being calibrated to allow for the minimum pressure required to operate the fluidic device and thereby provide a digital reading of the blood pressures.

22. The sphygmomanometer of claim 21 wherein said electrical means includes separate counters for recording diastolic and systolic pressures, each of said counters being connected to count all of the oscillating pressure pulses produced by the flip-flop device, and means for resetting each of the counters at the appropriate times corresponding to diastolic andsystolic pressures.

23. Blood pressure measuring apparatus comprising:

an inflatable cuff to be wrapped around the subjects extremity; v I

a specific volume container to be pressurized to the level of the inflated cuff while isolated'from the cuff;

means for pressurizing said cuff and said container;

means for releasing air from the cuff while maintaining the pressure in the cuff substantially equal to the pressure in the container;

a bistable fluidic flip-flop means connected to said container to process fluid from the container in a manner to produce asynchronous output pulses of substantially equal pressure increments;

pressure operated switch means responsive to said oscillating pressure increments;

display means including a systolic counter and a diastolic counter for counting the signals received from said oscillator switch means;

transducer means associated with said cuff. for detecting when the blood first rushes through an ar- 7 an electronic processor means for processing signals received from the transducer means to reset the systolic counter when a signal is received from the transducer means indicating that the cuff is at systolic pressure and to reset the diastolic counter each time a signal from the transducer means is received indicating that the pressure in the cuff is still in the systolic to diastolic range, said processor means including an electrical gate which receives signals from said transducer, a dynamic latch connected to said gate and said systolic counter for preventing further resetting of the systolic counter after the systolic event so long as signals are received by the latch from the gate indicating that the pressure is in the systolic to diastolic range, said latch means being adapted to reset upon cessation of such signals from the gate; and means for closing said gate upon the resetting of the latch. 24. The apparatus of claim 23 wherein said means for closing said gate includes a sequence latch connected to the gate and connected to receive a signal from said dynamic latch when it resets upon cessation of signals from the gate.

25. The apparatus of claim 24 wherein said means 26. The apparatus of claim 25 including means connected to said sequence latch to indicate when said cuff is deflating and to cause said latch to close said first mentioned gate except when the cuff is deflating.

27. A method of measuring blood pressure comprising the steps of:

applying pneumatic pressure to an inflatable cuff around a subject's extremity at a pressure sufficient to occlude arterial blood flow; applying pneumatic pressure to a specific volume container which is isolated from the cuff; processing fluid from the container through a bistable fluidic device having its output ports connected to its control ports so as to cause the fluid flow to oscillate between alternate restricted exhaust paths, each oscillation caused by substantially equal increments of pressure decrease occurring upon the passage of a given mass of the fluid through the device from the container; bleeding pressure from the cuff in a manner to maintain cuff pressure proportional to container pressure; counting the pressure increments to obtain a digital reading of the pressure in the container, and thereby the pressure in the cuff; and initiating the counting operation upon the receipt of signals related to the subjects blood pressure to thereby obtain digital readings of the pressure. 28. The method of claim 27 wherein said signals relating to blood pressure are obtained by detecting the Korotkoff sounds of the blood as cuff pressure decreases and blood commences to once more flow through the artery indicating the systolic blood pressure, and by detecting the cessation of the Korotkoff sounds which occurs when the artery is no longer occluded, thus indicating diastolic blood pressure, and utilizing the detected sound signals to initiate counting of said pressure increments to thereby obtain digital readings of systolic and diastolic blood pressure.

29. The method of claim 28 including the step of detecting the subjects pulse and combining it with said detected sound signals such that counting of said pres sure increments is not initiated until such times as a signal of the subjects pulse occurs at the same time as a sound signal is detected thereby reinforcing the accura- 

1. In a sphygmomanometer having an inflatable cuff to be wrapped around a subject''s extremity and pressurizing means for inflating the cuff, an improved means for indirectly determining blood pressure comprising: a specific volume container having an inlet means for pressurizing said container; fluidic means connected to said container to process fluid from the container in a manner to produce pressure pulses of substantially equal pressure increments; isolating means for maintaining the pressure in the cuff proportional to the pressure in the container and for preventing fluid flow from the cufF to the container; and means for counting the pressure increments to obtain a digital measure of the pressure in the container and thereby pressure in the cuff so that blood pressure can be determined upon receipt of signals related to the events in the indirect measurement of a subject''s blood pressure.
 2. The sphygmomanometer of claim 1 wherein said fluidic means includes a bistable fluidic flip-flop having an inlet port connected to the container, a pair of output ports stemming from a common junction leading from the inlet port, a pair of restricted exhaust paths leading from the output ports, a pair of control ports on opposite sides of said junction for deflecting fluid flow to one or the other output port, and a pair of flow restrictors each connecting an output port to one of the control ports to produce said pressure increments.
 3. The sphygmomanometer of claim 1: including means for detecting Korotkoff sounds which occur when the blood first rushes through an artery after the pressure in the cuff has been raised to a level to completely occlude the artery and pressure in the cuff has then been reduced to permit blood to begin to flow through the artery, and means for detecting the absence of Korotkoff sounds which occur when the artery is no longer obstructed; and wherein said counting means includes a counter for registering systolic blood pressure and a counter for registering diastolic blood pressure; and including a signal processor having means for utilizing the systolic event for operating the systolic counter so as to obtain a systolic blood pressure reading on the counter and means for utilizing the diastolic event to enable the diastolic counter to obtain a reading of diastolic blood pressure.
 4. The sphygmomanometer of claim 3 including means for detecting the subject''s pulse and means for utilizing the pulse signal with the Korotkoff signals so that the decision of systolic and diastolic pressures is made by correlating the Korotkoff signals and the pulse signals so that extraneous acoustical signals will not cause erroneous decisions.
 5. The sphygmomanometer of claim 4 including electrical means for counting and multiplying the pulse signals to obtain a pulse reading in beats per minute.
 6. The sphygmomanometer of claim 3 including means for resetting the systolic pressure counter when the Korotkoff sounds indicating the systolic event are first detected, and means for resetting the diastolic counter each time Korotkoff sounds are detected so that cessation of the sounds will indicate the diastolic event and will stop further resetting of the diastolic counter so that the diastolic counter will accumulate the count.
 7. The sphygmomanometer of claim 1 including: means for indicating when the pressure in the cuff is in the systolic-diastolic blood pressure range; wherein said counting means includes a counter for registering systolic blood pressure and a counter for registering diastolic blood pressure; means for resetting the systolic counter when the cuff pressure is at systolic pressure; and means for resetting the diastolic counter each time a signal is received from the indicating means that the cuff pressure is in said range so that when the signals cease at the diastolic event the diastolic counter continues to accumulate the pressure count.
 8. The sphygmomanometer of claim 7 including latch means for preventing resetting of said systolic counter once systolic pressure is reached and so long as periodic signals are received by the latch means indicating that the cuff pressure is in said range.
 9. The sphygmomanometer of claim 1 wherein said isolating means includes a diaphragm having one side forming the wall of a chamber in communication with the container and having its other side forming a wall of the chamber in communication with the cuff, said diaphragm supporting a valve member for bleeding pressure from the cuff as the pressure is bled from the container.
 10. The apparatus of claim 1 including signaling means for indicating when the fluidic means is operating.
 11. The sphygmomanometer of claim 1 wherein said container is connected to be pressurized as the cuff is being inflated, and including a pneumatic diode connected between the cuff and the container permitting flow into the cuff but preventing flow out of the cuff, the diode having significant internal resistance to flow such that air flows smoothly into the cuff.
 12. Blood pressure measuring apparatus comprising: an inflatable cuff to be wrapped around the subject''s extremity; a specific volume container to be pressurized to the level of the inflated cuff while isolated from the cuff; means for pressurizing said cuff and said container; means for bleeding fluid from the cuff while maintaining the pressure in the cuff substantially equal to the pressure in the container; a bistable fluidic flip-flop means connected to said container to process fluid from the container in a manner to produce decreasing asynchronous output pressure pulses of substantially equal pressure increments; pressure operated switch means responsive to said oscillating pressure increments; display means including a systolic counter and a diastolic counter for counting the signals received from said oscillator switch means; a microphone means associated with said cuff for detecting the Korotkoff sounds which occur when the blood first rushes through an artery after the pressure in the cuff has been raised to a level to completely occlude the artery and the pressure in the cuff has then been reduced to permit blood to begin to flow once more through the artery; and an electronic processor means for processing signals received from the microphone to reset the systolic counter when a signal is received from the microphone indicating that the cuff is at systolic pressure and to subsequently reset the diastolic counter when signals from the microphone are present as defined by Korotkoff until the cessation of such signals indicating that the pressure in the cuff is at diastolic pressure.
 13. The apparatus of claim 12: including a transducer means for detecting the subject''s pulse; and wherein said processor means includes means for processing the pulse signals from the transducer in a manner such that signals from the microphone must coincide with the pulse signals before said counters can be reset.
 14. The apparatus of claim 12 wherein said processor means includes an electrical gate which receives signals from said microphone means and said transducer means and which will not open unless both signals are present at approximately the same time, the output signal from said gate being utilized to initiate resetting of said counters.
 15. The apparatus of claim 14 wherein: said processor means further includes electrical means for processing the pulse signals received from the transducer to determine the subject''s pulse in beats per minute; and said display means further includes a counter for counting and displaying the subject''s pulse directly in beats per minute.
 16. The apparatus of claim 12 wherein said processor means includes dynamic latch means connected to said microphone and said systolic counter for preventing further resetting of the systolic counter, after the initial resetting indicating systolic pressure, so long as signals from the microphone are received by the latch means in a time interval slightly greater than the interval between two periods of the subject''s nominal heart beats.
 17. The apparatus of claim 12: including a restrictor in a tube connecting the container and the fluidic device and a pressure differential responsive switch exposed to the cuff pressure and the pressure downstream from the restrictor to detect when the pressure in the cuff is falling; and said processor means includes means for processing the signal received from said differential switch to prEvent resetting of the counters after the occurrence of the systolic and diastolic events until such time as a signal is received from said differential switch indicating that the pressure in the cuff is once more falling.
 18. The apparatus of claim 17 wherein the means within said processor for preventing resetting of the counters until a proper signal is received from said differential switch includes latching means which receives a signal upon indication of the diastolic event and prevents the resetting of said counters until such time as an appropriate signal is received from said differential switch.
 19. The apparatus of claim 12 including means for preventing the processor means from providing signals to reset the counters after the diastolic event during the deflation cycle and until a new deflation cycle is initiated.
 20. The apparatus of claim 12 including signalling means for indicating when Korotkoff sounds start and cease.
 21. A sphygmomanometer comprising: an inflatable cuff to be wrapped around the subject''s extremity; pressurizing means connected to inflate the cuff; a known volume container connected to said pressurizing means to be pressurized simultaneously with the inflation of the cuff; a pneumatic diode in the line between the pressurizing means and the cuff permitting fluid flow into the cuff but preventing fluid flow from the cuff to the pressurizing means or to the container; a bistable fluidic flip-flop device having an input port connected to said container, the device having a pair of output ports connected to a common junction in communication with the input port, a restricted exhaust path leading from each of said output ports, and a control port on opposite sides of the common junction to oscillate the flow between the two outlet ports upon the application of alternate pneumatic control signals, each control port being connected by a restrictor to a respective one of said outlet ports so that as the pressure rises within an outlet port a pressure pulse is created for oscillating the fluid flow to the other outlet port; an interface device comprising a housing have a flexible diaphragm dividing the housing into a pair of chambers, one chamber being connected to the reservoir and the other chamber being connected to the cuff, an exhaust port being formed in a wall of the chamber connected to the cuff, and a valve member carried by the diaphragm for permitting air to be bled from the cuff at a rate to maintain the pressure in the cuff equal to that of the pressure in the reservoir; a microphone means for detecting Korotkoff sounds through the artery as the pressure from the cuff is bled from a point above systolic blood pressure; electrical means for counting the oscillating pressure pulses produced by the fluidic flip-flop device upon receiving a signal from the microphone that Korotkoff sounds corresponding to systolic blood pressure have been detected; electrical means for counting the pressure pulses produced by the fluidic flip-flop upon receiving a signal from the microphone corresponding to diastolic blood pressure; and the counting means being calibrated to allow for the minimum pressure required to operate the fluidic device and thereby provide a digital reading of the blood pressures.
 22. The sphygmomanometer of claim 21 wherein said electrical means includes separate counters for recording diastolic and systolic pressures, each of said counters being connected to count all of the oscillating pressure pulses produced by the flip-flop device, and means for resetting each of the counters at the appropriate times corresponding to diastolic and systolic pressures.
 23. Blood pressure measuring apparatus comprising: an inflatable cuff to be wrapped around the subject''s extremity; a specific volume container to be pressurized to the level of the inflated cuff while isolated from the cuff; means for pressurizing said cuff and said container; mEans for releasing air from the cuff while maintaining the pressure in the cuff substantially equal to the pressure in the container; a bistable fluidic flip-flop means connected to said container to process fluid from the container in a manner to produce asynchronous output pulses of substantially equal pressure increments; pressure operated switch means responsive to said oscillating pressure increments; display means including a systolic counter and a diastolic counter for counting the signals received from said oscillator switch means; transducer means associated with said cuff for detecting when the blood first rushes through an artery after the pressure in the cuff has been raised to a level to completely occlude the artery and the pressure in the cuff has then been reduced to permit blood to begin to flow once more through the artery; and an electronic processor means for processing signals received from the transducer means to reset the systolic counter when a signal is received from the transducer means indicating that the cuff is at systolic pressure and to reset the diastolic counter each time a signal from the transducer means is received indicating that the pressure in the cuff is still in the systolic to diastolic range, said processor means including an electrical gate which receives signals from said transducer, a dynamic latch connected to said gate and said systolic counter for preventing further resetting of the systolic counter after the systolic event so long as signals are received by the latch from the gate indicating that the pressure is in the systolic to diastolic range, said latch means being adapted to reset upon cessation of such signals from the gate; and means for closing said gate upon the resetting of the latch.
 24. The apparatus of claim 23 wherein said means for closing said gate includes a sequence latch connected to the gate and connected to receive a signal from said dynamic latch when it resets upon cessation of signals from the gate.
 25. The apparatus of claim 24 wherein said means for closing said gate further includes a second gate connected between the dynamic latch and the sequence latch, the second gate when closed preventing signals from the dynamic latch from reaching the sequence latch, and a systolic timing circuit connected to said dynamic latch and said second gate to open said second gate after an interval of time slightly less than the time between the systolic and diastolic events so that said sequence latch for closing the first mentioned gate will only receive a signal corresponding to a true diastolic event.
 26. The apparatus of claim 25 including means connected to said sequence latch to indicate when said cuff is deflating and to cause said latch to close said first mentioned gate except when the cuff is deflating.
 27. A method of measuring blood pressure comprising the steps of: applying pneumatic pressure to an inflatable cuff around a subject''s extremity at a pressure sufficient to occlude arterial blood flow; applying pneumatic pressure to a specific volume container which is isolated from the cuff; processing fluid from the container through a bistable fluidic device having its output ports connected to its control ports so as to cause the fluid flow to oscillate between alternate restricted exhaust paths, each oscillation caused by substantially equal increments of pressure decrease occurring upon the passage of a given mass of the fluid through the device from the container; bleeding pressure from the cuff in a manner to maintain cuff pressure proportional to container pressure; counting the pressure increments to obtain a digital reading of the pressure in the container, and thereby the pressure in the cuff; and initiating the counting operation upon the receipt of signals related to the subject''s blood pressure to thereby obtain digital readings of the pressure.
 28. The method of claim 27 wherein said signals relating to blood pRessure are obtained by detecting the Korotkoff sounds of the blood as cuff pressure decreases and blood commences to once more flow through the artery indicating the systolic blood pressure, and by detecting the cessation of the Korotkoff sounds which occurs when the artery is no longer occluded, thus indicating diastolic blood pressure, and utilizing the detected sound signals to initiate counting of said pressure increments to thereby obtain digital readings of systolic and diastolic blood pressure.
 29. The method of claim 28 including the step of detecting the subject''s pulse and combining it with said detected sound signals such that counting of said pressure increments is not initiated until such times as a signal of the subject''s pulse occurs at the same time as a sound signal is detected thereby reinforcing the accuracy of the system.
 30. The method of claim 29 including the step of counting the signals corresponding to the subject''s pulse and electrically converting such count into beats per minute.
 31. The method of claim 27 including the steps of counting the pressure pulses with two digital counters; resetting one of said counters with the receipt of a signal corresponding to systolic blood pressure; and resetting the other of said counters with each Korotkoff signal until absence of signal corresponding to diastolic blood pressure. 